Ultrasonic vibration driving type thermal printer

ABSTRACT

A thermal printer in which dye is transferred from a film to a receiver in response to heat including a thermal head assembly having a plurality of heating elements. The thermal head comprises a vibration device adapted to induce a vibration wave in the heating elements which move in one direction in time. The heating elements are supported by the vibration device and, as they frictionally engage the film, cause the film and the receiver to move in the opposite direction.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a thermal printer in which heatingelements are formed on a vibration device such as an ultrasonic vibratorwhich sets up a vibration wave that directly drives a color dye film andan image receiver.

DESCRIPTION OF THE PRIOR ART

Referring now to FIG. 1, there is shown a printing section of aconventional thermal printer. FIGS. 2a and 2b in combination show oneexample of the structure of a thermal head illustrated in FIG. 1. Inthese figures, the thermal head includes a multiplicity of heatingelements 2 formed on the underside of a substrate 1 composed of ceramicor the like, and conductive leads 3. These leads conduct direct currentto the heating element causing such heating elements 2 to produce heat.A media unit 4 consisting of a color dye film 4a and an image receiver4b moves as a platen roller 5 rotates while being in contact with theheating elements 2 of the thermal head TH.

The heating elements 2 are selectively energized and current flowsthrough a desired conductive leads 3, thereby causing heat to bedelivered to the film 4a. As a result, the color dye in the film 4asublimates and transferred to the image receiver 4b. At the same time,the media unit 4 is moved with respect to the thermal head by TH therotating action of the platen roller 5.

In the above-described conventional thermal printer, the media unit 4and the platen 5 are moved in such a way that the thermal head THremains stationary, so a slide condition always exists between the uppersurface of the film 4a and the heating elements 2.

On the other hand, in order to obtain a high-quality print, it isnecessary for the heat produced by the heating elements 2 to bepropagated through the film 4a to the image receiver with highefficiency, uniformity and constant stability. Accordingly, the thermalhead TH has to apply high pressure to the media unit 4 and the platenroller 5. It is not an easy thing, however, to maintain the slidingcondition of the media unit 4 with respect to the thermal head assemblyTH under such high pressure.

Special materials are coated on the upper layer of the film, in contactwith, the thermal heat to maintain the favorable non-sticking conditionbetween the media unit. These materials also must have desired heattransmission properties. It is difficult, provide slipping layers whichhave both of these properties. Furthermore, in some cases, the coatingmaterials peel off the film and adhered to the image receiver.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to obviatethe above-described defects and to provide a thermal printer in whichthe media unit moves without undergoing any sliding action with respectto the thermal head during printing to thereby obtain favorable printquality.

To accomplish the aforementioned object, a thermal printer according tothe present invention comprises vibration device adapted to induce atraveling vibration wave in the heating elements. The vibration wavetravels or moves in one direction in time. The heating elements aresupported by the vibration device, and, as they frictionally engage thefilm, causes the film and receiver to move in a predetermined direction.

When causing the vibration device to generate the traveling wave whichmoves in one direction in time, the moving members, that is, the film,image receiver and platen, which is brought into contact with thevibration device, move in a direction opposite to the direction of thetraveling of the synthesized wave by means of the propelling forceimposed by the heating elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one examle of a thermal head assembly of a conventionalthermal printer;

FIG. 2a is a sectional view of the thermal head;

FIG. 2b is a plan view of a thermal head of FIG. 1;

FIG. 3 is a schematic showing the first embodiment of a thermal printeraccording to the present invention;

FIG. 4 is a schematic diagram showing the second emodiment of anotherthermal printer according to the present invention;

FIG. 5 is a diagram for explaining the operation of the embodiments ofFIGS. 3 and 4; and

FIG. 6 is a schematic diagram showing a third embodiment of a thermalprinter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described withreference to FIGS. 3 to 6.

FIG. 3 is a schematic showing the first embodiment of a thermal printeraccording to the present invention. Like components are designated withthe same reference numerals as those in FIG. 1. In FIG. 3, the thermalhead is equipped with a cylindrical vibration device 6 a multiplicity ofheating elements 2 arranged in a row and the conductive leads 3 forconducting the electric current through the respective heating elements2. The vibration device 6 comprises a cylindrical vibrator 8 composed ofa piezo-electric material and a surrounding resilient member 7. Theheating elements 2 and the conductive leads 3 are formed on the outersurface of the resilient member 7 so as to be in contact with the colordye film 4a. A traveling wave is induced in the heating elements 2.

FIG. 4 shows the second embodiment of the present invention. Thedifference between the second embodiment and the first embodiment isthat the vibration device comprises a resilient member 7 and a vibrator8 formed of the piezo-electric material. On the lower surface of theresilient member 7 are a multiplicity of the heating elements 2 and theconductive leads 3. A traveling wave is induced in the heating elements.

In a traveling wave driving system which can be used in the presentinvention, a vibration wave moving in one direction in time is producedby a vibration device. The device includes a resilient member fixed to avibrator made of the piezo-electric elements such as piezo-electricceramic or the like. The moving member when it comes in facing-contactwith the vibration member is forced to move. Traveling wave systems arewell known. For a more complete disclosure of such systems and theircomponents, see U.S. Pat. Nos. 4,562,374, 4,678,956, 4,692,649,4,692,650 4,693,651, and 4,692,672.

In the above-described two embodiments (FIGS. 3 and 4), the vibrationdevice 6 of the thermal head is adapted to generate the traveling wave;the media unit 4 and the platen 5 which are brought into facing-contactwith the vibration member 6 are forced to move; as a result, separatedriving forces are not imposed to the platen 5. However, if the film 4ais soft, the heating elements 2 dig into the film, and sometimes theheating elements 2 penetrate the film 4a, whereby the driving force isnot sufficiently transmitted to the moving member. As one of the methodsfor solving this problem, it is helpful that the platen 5 besimultaneously rotated by driving means of any type together with themedia unit 4.

This traveling wave driving system which induces a traveling wave in theheating elements 2 will not be explained in connection with FIG. 6. Thevibrator 8 composed of the piezo-electric material and the resilientmember 7 formed on the outer surface thereof are combined to constitutethe vibration device 6. The heating elements 2 and the conductive lead3, which are formed on the outer surface of the resilient member 7, arearranged such as to come in contact with the moving member, viz., themedia unit 4 and the platen 5. With this arrangement, as is well known(see the above-cited U.S. patents) when the moving waves which travelsin one direction is excited on the vibration member 6, each point of thesurface of the vibration device 6 decribes a locus of points forming anellipse. FIG. 5 schematically shows this situation. In FIG. 5, since theelliptical locus rotates in the anticlockwise direction, the movingmember--the media unit 4 and the platen 5--is forced to move in thedirection indicated by arrow by the propelling force produced in thedirection opposite to the direction of the travel of the synthesizedwave.

The driving means of FIG. 6 can be used with the FIG. 3 or FIG. 4embodiments. In this figure, signals giving instructions of a drivingvelocity to the vibrator 8 are branched off and are then supplied to amotor 9 for rotating the platen 5. The motor 9 rotates to drive theplaten roller 5 so that the platen rotates at the same velocity in thesame direction as those of the media unit (film and receiver) 4 which isforced to move by the traveling wave produced by the vibration device 6.Accordingly, the relative velocity of the platen 5 to the media unit 4becomes zero, and the driving forces from the thermal head to the movingmember becomes zero or extremely small.

ADVANTAGES

According to the present invention, the media unit and the platen rollerare rotated by the traveling vibration on wave excited in the vibrationdevice, and hence it is possible to apply a large pressure to thethermal print head without creating problems noted above. Further,creases cannot be produced on the film. Moreover, the distance in whichthe ink film and the platen are moved for each image pixel becomes moreuniform, so it is posible to obtain images having quality higher thanthat of the conventional thermal printers.

Because no sliding condition exists between the thermal head and thefilm, wear of the thermal head is also greatly be reduced.

The invention has been descirbed in detail with particular reference toa certain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

I claim:
 1. In a thermal printer in which dye is transferred from a filmto a receiver in response to heating including:a. a thermal head havinga plurality of heating elements arranged in a predeterminedconfiguration and selectively energized on the basis of print data; b.said heating elements being brought into frictional contact with thefilm having heat transferable color dye for causing the color dye to betransfered from the film to the receiver by means of the heat producedfrom the selectively energized heating elements; and c. a platen forsupporting the film and the receiver,i. an improvement in the thermalhead comprising: ii. a vibration device having an elastic member formedon said heating elements, said vibrating device including means forvibrating said elastic member which induces a vibration traveling wavein said heating elements; and iii. the induced vibration wave in saidheating elements causes the film and receiver to move in a predeterminddirection.
 2. Thermal printer as claimed in claim 1 wherein said platenis a drum which is rotated by the film and receiver as they are drivenin the predetermined direction.